Various designs have been suggested for providing a collet and chuck assembly for securing an end mill tool therein against axial movement of the tool out of the assembly and against rotation of the tool with respect to the assembly and collet.
Such designs generally include an aperture through the collet, with a movable pin mounted therein for engaging a flat surface on the end mill shank. Mounting and retaining the pin suitably has been a problem in the prior art collets, except for the Non-Pullout Collet Patent discussed later. The pin should be easily movable to secure and release the tool, while resisting accidental separation of the pin from the collet. However, for service or repair, the pin should be quickly and easily released. Further, the mounting and retaining mechanism should not be on the external surface of the collet, to minimize the chance of damage thereto.
Cutting tools for chuck assemblies may range from only slightly smaller than the bore in the chuck to substantially smaller, with the thickness of the collet wall varying accordingly. An ideal collet for an end mill is not dependent on a particular wall thickness. More particularly, a very thin-walled collet (i.e., where the tool shank is almost as the chuck bore), must suitably accommodate the pin and its retention system, while allowing limited pin movement.
One approach suggested in the prior art was to provide the outer collet body and pin with a groove, in which an external spring retaining ring is mounted.
Another prior art approach was to drill a hole through the collet body perpendicular to and intersecting the pin aperture. The movable pin is provided with a hole also, and a roll pin is inserted into the aligned pin hole and collet body hole to retain the movable pin.
Typically, such designs have at least one of the following disadvantages: expensive to manufacture; time-consuming, difficult and/or expensive to assemble; parts, other than the collet body and the pin itself, which are on the external surface of the collet and subject to wear and destruction.
Examples of such collets are shown in U.S. Pat. Nos. 3,195,909; 3,425,705; 3,618,962; and others.
The collet design in the referenced Non-Pullout Collet Patent overcomes many of the disadvantages and limitations of the prior art. However, for thin-walled collets, the design in the Non-Pullout Collet Patent does not suffice. The pin and collet walls are simply shrunk to a thickness which does not allow an undercut and stepped radial aperture, respectively to allow a radially-movably mounted pin.
It is thus apparent that there are disadvantages and limitations of the prior art collets for retaining an end mill tool. Lacking is a collet which is reliable and economical to manufacture, while quickly engaging and disengaging an end mill-type tool without external parts to be damaged. Other disadvantages and limitations of the prior art collets and chuck assemblies will be apparent from the following description of the present invention.